Radio receiving system



July '21, 1925. 1,546,878

E. F. W. `ALEXANDERSON RADIO RECEIVING SYSTEM Filed June -7, 19:21

Inventor: Emst wlgxgmndevsqn,

by 4&14

una PATENT Genio.

ERNST li. W. ALEXANDER/SON', 0F SCHENEOTADY, lllrEi/V YORK, ASSIGNOR .TOI GENERAL ELEGTHC GOMPAN'Y, A CORlBORATIQN OF NEX/V YORK.

RADIC) .'{tiGEIVING SYSTEM.

application filed fune i921.

To cZZ wiz-om it' may concern.'

Be it known that'l, ERNST ll". idf. ftlinmnf Schenectady, Stateot New York, have invented certain new and useful improvements in Radio Receiving Systems, of which the iollowingis a specification.

My present invention Vrelates to radio re ceiving; systeniaand incre particularly to a system which permits oit the simultaneous reception of a `plurality ot signals upon a single receiving antenna.

lIt has been discovered that it a long horizontal receiving antenna extending in the general direction oi the transmission oi si gnaling Waves to be received is grounded at both ends, vsignaling currents produced in the antenna by Waves coming from any particular ti'ansiiiitting station will be strongest at the end oi the antenna farthest from the transmitting station lWhile currents proy duced by waves coiningl troni the opposite direction Will be a ininiinuni at that point.

Such an antenna is preferably constructed with distributed constants ol such value that the current Wave therein travels at 'the same velocity as the other Wave. lt is also pref erably' aperiodic so that the strength oi the signaling currents produced therein is substantially independent of the Wave length.

One oli-the objects of my present invention is to provide method oli and means ior utilizing.;` an antenna of the :torni described 'for the simultaneous reception ci a plu-- rality o'l' signals of different Wave lengths.

l/Vhilc a long,r horizontal antenna such as that described has decided unidirectional j"propert1cs, mathematical analysis indicates and experience shows that at the end furthest frointhe transmitting station small currents Will under seine conditions be pro- 1 over the antenna a vvave component of the of the aiiteniaa may not be the best iir'- pedance to eiiiploy iu the ground connection of the antenna nearest the tr isiiiittinn' station; the :tore in. order to a in this object oit my invention l provide an in pedance which is preferably adjustable in dei' that the best operating conditions may readily be obtained. @ne forni. vrci impedance which has been .found in practice to be convenient consists of a resistance and a snies 'tuned circuit of louT` impedance'. The object of this. series tuned circuit is to reflect back proper inagnitiidet and phase to neutralize the sin-all undesired Waves inentionedi By slightly off tuning,w this circuit sniall duced by Waves coming from the opposite' direction even though the end of the antenna nearest the transmitting station is grounded through a resistance approxin mately equal to the .sui-ge impedance oi', the antenna so that no reflection can occur.

A more specific object of iny invention is to provide ineans for eliminating,r the eiliect upon the receiving apparatus ot' sniall undo sired currents such as those produced in the antenna by' reason ot the tact mentioned above, as well as by other conditions. 'Under these circumstances the surge impedance amount ot capacitive reactance or inductive reactance as may be desired inay be introduced to give the desired reiectioii g in other Words, by suitable adjustment el the terininal impedance oi the antenna it isi possible to prevent any undesired 'retlection and at the saine tinie produce a reflection et the proper nature to eliminate disturbing eiiiects. An adjustment of this nature; however, will be most effective for one particular Wave length to be received. Whein therefore, as in the present case, it is de siied to receive several Wave lengths upon the saine antenna, it is necessary to provide `separate means for adjusting the reiiection to secure the best results i'oi each Wave length to be received. This eii'ect ina-y be obtained by using a separate series tuned circuit in series with the resistance ior eac-h of the Wave lengths to be received. lilllire. the Wave lengths are quite Widely separated the series tuned circuit which gives the right. value ot refiection for one Wave length. will be of such high impedance for cui-rents of other Wave lengths that it Will have siibstann tially no ei'i'ect in so far as the other Wave lengths are concerned.

The novel features which l believe .to be characteristic oi? iny invention are set forth with particulaiity in the appended claims, iny invention itself, however, both as to Aits" organization and method of operation hill?4 best be understood by reici'enc-e to the tot lowing description taken in connection with Ll O mami

long horizontal antenna which is preferably made up of at least two parallel wires 1 and 2, the opposite ends oi which are grounded at 3 and 4. rlhis antenna is preferably sov constructed, or its constants so adjusted that current waves flowing therein will travel along' its length at the same velocity as that of the signaling' waves in space so that the current waves will gradually grow in amplitude as they travel along the conductor. lit it is desired to receive signals which approach the antenna 'from the end the amplitude o'lt the currents set up .in the antenna at l by the desiree signaling waves will he extremely small while at the end L1 the amplitude o'l these currents will he a maximun'i. lt may, however, be more oonvenient to vlocale the receiving` station at the end 3. ln order to permit ot' such a location of the receiving station the antenna conductors may he employed as a transmis sion line vFor transmitting` the desired signaling currents trom end 4: to end One way in which this result may he accomplished is lo provide at the end 4. a transformer system made up ot a primary winding l and a secondary winding G. The primary 5 of this transformer is connected in series with the ground connection and the two terminals ot the secondary 6 connected re spectiroly to the conductors l and 2, the middle point 7 et this secondary boing con'- neeted to ground through the primary 5.

lly means oli the connection described, Signaling' currents lio'wing in the same direction in conductors 1 and t2xtoward the end 4l of the antenna flow in parallel to ground through the primary winding 5, and are transferred back upon conductors l and 2 so :is to liow in opposite directionsthrough these two conductors. The conductors 1 and 2 thus torni the two sides of `a transmission line which is closed at the receiving station through primary winding 8 et a transtormerl This priniary winding' S has asso oiated therewith as many secondary windJ inns l), 10, 11 as-there are separate signals which are to he received upon the antenna.l

Each of these secondary windings is associated with a resonant circuit 12,13, 1.11-, by

.means of which the different signaling ourrents to be received are selected and impressed upon the separate receiving sets l5, 16', 17. The signaling currents transmitted from the end 4 et the antenna flow through the two halves of the primary 8 in series. Gsrrents received upon 'the antenna, however, Jrom waves traveling from end e toward end 3, dow through the `two halves of the primary 8 in parallel to ground, and hence produce equal and opposite effects in the windings 9,-10, and 11. As a result the receiving; apparatus will be unaffected by such currents.

ln order to prevent the reflection over Landers the antenna conductors of currents flowing to ground at 3, a variable resistance 18 is provided in the ground connection which should be made approximately equal to the surge impedance of the antenna. I also provide in series with this resistance as many series 'tuned circuits 19, 20 and21 as there are separate receiving sets. Each of these series `tuned circuits is made up of an inductauce Q2 and capacity 23,`one or both ot which should be adjustable, and an adjustable resistance 24.

In adjusting;- the system, circuit 19, for example, may be adjusted to secure the desired neutralization in the receivingapparatus 15. Unless the signals received in the y ditlierent receiving sets are of closely adjacent wave lengths this adjustment will not give the best results for the operation of receivingsets 1G, 17. Circuit 20, therefore, may be adjusted to secure the desired results in receiver 1'6 and the circuit 21 may be adjusted to secure the desired results in receiving set 17. It the signals are of consideral ly diiiorent wave length, these separate adjustments will produce substantially no effect upon each other, the resistance and reactance ot the entire circuit between joint Q5 and ground for each wave length 'depending almost entirely upon the resistance and reactance of the circuit which is approximately in tune for that wave length.

vWhile I have shown and described the preferred embodiment ot my invention it will be apparent that my inventionl is by no means limited to the particular arrangement shown, hut that many variations therein may be made without departing from the scope of my invention as set forth in the appended claims.

That I claim as new and desire to secure by Letters Patent of the United States, isz- 1. A receiving system for radio signals comprisingl a substantiallyI horizontal rc ceiving antenna which has a ground connecn tion at one end including a resistance substantially equal to the surge impedance of said antenna, a plurality of receiving sets associated with said antenna and a plurality of series tuned circuits in said ground connection.

2. A receiving system for radio signals comprising a substantially horizontal receiving` antenna which has a ground connec tion at one end including a resistance substantially equal to the surge impedance of said antenna, a plurality of receiving sets associated with said antenna and a plurality ot series tuned circuits of different resonant frequencies in said ground connection.

8. A. receiving system for radio signals comprising a substantially horizontal receiving antenna which is grounded at both ends, moans at one end of said antenna for preventing any undesired reflection ot elec tric Waves traveling` along said antenna in a direction diti'crent troni that of the waves to be received, plurality or' receiving sets associated Wih said antenna, and means for producing a reflection. of waves .in said an` tenna to elin'iinate the effect in each of said receiving sets of waves traveling along said antenna in a direction dinierent from that ol the wave to he received.

l. i receiving system torujadio signals coniprisinga long horizontal receiving` antenna, means for conveying signaling currents ironi a point in said antenna Where the signals to he received are strongest to a distant receiving station, a plurality of receiving sets at the receiving station, means at another point in said antenna -tor preventing any undesired reilection of electric Waves traveling along said antenna in a direction dili'erent from that of jthe Waves to bereceived., and means for producing` a reflection ot Waves in said antenna to eliminate the eil'ect in each of said receiving sets of waves 'traveling along said antenna in a. dircction different 'from that ot the Waves to he received.

A. receiving system Yfor radio signals comprising a long horizontal receiving antenna, moans for conveying signaling eur-` reni-s ilroi'n a selected point in said antenna Where desired signals are strongest to a distant receiving' station, a plurality otreceiving sets at the receiving station, a ground connection at another point in said antenna including a. resistance substantially equal to the surge impedance of the antenna, and av nating the effect in each of the receiving sets ot any undesired currents normally flowing' at "the selected point by producing a reflection over the antenna from another point of? currents ofthe saine frequencies and et equal magnitude, and opposite phase to the'undesired currents 7. The method of eliminating the eect in a long` horizontal receiving antenna of undesired currents at a selected point Where signaling currents from a pluality of desired stations have a desired relation to other currents in the antenna which consists in reflecting over the antenna from another point'a plurality of currents of equal inagnit-ude and opposite phase to the undesired currents.

ln Witness whereof, l have hereunto set my hand this (ith. day of June, 1921.

ERNST F. lV. ALEXANDERSON.

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